1. Technical Field
The present invention is directed toward farm implements, and more particularly toward an adjustable attachment for mounting a tool to a tow bar on a tractor
2. Background Art
Attachments for mounting tools to a tow bar on a drawing vehicle such as a tractor are well known in the art. Typically these attachments consist of an elongate shank having a first and a second end, a bracket for fastening the first end of the shank to a tow bar and structure for fastening a farming tool at the second end of the shank.
As is well known in the art, in order to obtain the most efficient function from a wide variety of soil cultivation and fertilization equipment an adjustment device must be provided with the farm tool attachment for adjusting the position of the tool on the attachment relative to the tow bar. For example, it is known in the art that tools for distributing gaseous fertilizers such as anhydrous ammonia into soil are most effective when the tools pass through the soil with a minimum amount of cracking and fracturing of the soil, the cracks and fractures providing a path for the fertilizer to escape into the atmosphere. Thus, the prior art teaches an adjustment device for adjusting the tools relative to the tow bar to minimize the disruption of the soil.
A specific example of a structure for distributing gaseous fertilizers into soil known in the art consists of a vertically oriented shank having a first and a second end, a bracket for fastening the first end of the shank to a tow bar and a fertilizer distributor attached to the second end of the shank. The fertilizer distributor may be, for example, a "V"-shaped, plow or blade structure formed by two elongate leg members each having a first and a second end, the first ends joined to form the apex of the V and the second ends spaced apart to form the mouth of the V. The "V"-shaped blade is attached to the second end of the shank at the apex of the V. Metal tubes for distributing fertilizer have outlets near the second ends of the legs.
It is known that when the "V"-shaped blade is not adjusted to form a plane substantially parallel to a plane formed by the surface of the soil the effective cross-sectional area of the path formed by the blade and shank is greater than the cross-sectional area of the actual shank and blade. Thus soil disruption is increased and the formation of excessive cracking and fissures results which allows for highly undesirable escape of gaseous materials.
To address this problem, prior art devices have provided an adjustment device for leveling a "V"-shaped blade. One such prior art adjustment device for leveling a "V"-shaped blade provides the vertical shank with a pivot point at the bracket and an adjustable stop for halting the pivot of the shank at the top of the bracket. Using this structure the "V"-shaped blade may be set in a plurality of fixed positions relative to the tow bar.
A second prior art adjustment device for leveling a "V"-shaped blade consists of a vertical shank divided into lower and upper shank parts. The lower and upper shank parts are joined by a pivot joint. The lower shank part further includes opposing arcuate grooves located away from the pivot joint. A threaded bolt is fixedly secured within the upper shank part such that the shaft of the threaded bolt fixedly engages the upper shank part. The lower shank part may be pivoted relative to the upper shank part when the threaded bolt is in an untightened position and the grooves will slide over the threaded bolt. The threaded bolt can be tightened to frictionally secure the lower shank part relative to the upper shank part.
The first prior art structure has numerous drawbacks. First, the distance between the tow bar and the "V"-shaped blade (known as the trash clearance) results in a significant torque being applied to the adjustable stop as the "V"-shaped blade is driven through the soil. This torque is significantly increased if the "V"-shaped blade or the shank strike a rock or other obstruction. In addition, the adjustable stop is in an exposed position as it rides on the top of the tow bar, thus being susceptible to being forced out of adjustment or damaged by crops or other obstructions as the fertilizer distributor is used.
To minimize the moment arm for the blade and thereby reduce the stress on the adjustable stop and the pivot point prior art designers have reduced the length of the shank. However, this solution merely exacerbates the potential interference with the adjustable stop as more obstructions are likely to be encountered closer to the ground. Moreover, this option may not be available if the height of the tow bar cannot be reduced.
The second type of prior art leveling adjustment is deficient because it relies upon frictional forces to pivotly secure the lower segment relative to the upper segment. Frictional forces are inadequate to pivotly secure the lower segment relative to the upper segment when the tool engages a significant obstruction such as a large rock. Moreover, the degree of tightening of the bolt necessary to maximize the frictional force requires great effort in the field and may lead to stripping the threaded bolt and thus failure of the adjustment device.
Prior art fertilizer distributors have problems in addition to those discussed above with respect to leveling adjustments. Most notably, the fertilizer distributing tubes of the prior art structures typically are metal tubes welded or bracketed to the shank or the "V"-shaped blade. Those structures welding the metal tubes to the shank or "V"-shaped blade have the problem that the tubes are difficult to replace once they are damaged or worn. Those structures using brackets to secure the metal tubes permit the brackets to protrude into the soil as the fertilizer distributor is run through the soil, exposing the brackets to wear and increasing the cross-sectional area of the path as the distribution tool passes through the soil.